A key to coexistence of a licensed-assisted access (LAA) system, that is, a Long Term Evolution-Unlicensed (U-LTE) system, and a Wireless Fidelity (WiFi) system is to effectively avoid co-channel interference caused when the two systems simultaneously occupy an unlicensed channel, that is, an unlicensed spectrum.
A network element in the LAA system includes a base station, and a network element in the WiFi system includes a WiFi access point (AP). The base station uses a carrier sense/clear channel assessment (CS/CCA) mechanism to detect whether a current unlicensed channel is occupied. In the mechanism, the WiFi AP can detect only a signal whose signal strength is greater than or equal to a detection threshold, and different detection thresholds are used when the WiFi AP detects an intra-system signal (that is, a WiFi signal) and an inter-system signal (such as an LAA signal). An example in which a system bandwidth is 20 MHz (megahertz) is used. A detection threshold used when the WiFi AP detects a WiFi signal is −82 dBm, and a detection threshold used when the WiFi AP detects an LAA signal is −62 dBm. If signal strength of an LAA signal is in the range of −82 dBm to −62 dBm, the WiFi AP cannot detect the LAA signal. As a result, when the base station sends, on the unlicensed channel, an LAA signal whose signal strength is in the range of −82 dBm to −62 dBm, the WiFi AP cannot effectively avoid using the unlicensed channel. Finally, co-channel interference may be caused because the base station and the WiFi AP simultaneously send a signal on the unlicensed channel.
To resolve the foregoing problem, the base station may send a channel reservation signal on the unlicensed channel. The channel reservation signal uses a WiFi frame format. In this way, the WiFi AP considers the LAA system to which the base station belongs as an intra-system, and therefore sets the detection threshold to −82 dBm. Therefore, the WiFi AP can detect the LAA signal whose signal strength is in the range of −82 dBm to −62 dBm, and when the LAA signal whose signal strength is in the range of −82 dBm to −62 dBm occupies the unlicensed channel, the WiFi AP can avoid using the unlicensed channel. Therefore, a probability of co-channel interference is reduced.
In the foregoing channel reservation signal sending process, the base station sends the channel reservation signal each time the base station needs to occupy the unlicensed channel. This causes resource waste.